Photosynthetic analysis of mid-vein and leaf lamina in high-yield hybrid rice in fields during senescence

Abstract

Previous studies on rice (Oryza sativa L.) have shown that different components of the photosynthetic apparatus are not uniformly synthesized or degraded during senescence. However, most of these senescence-related studies focused on leaf lamina, while few have addressed functional aspects on chloroplasts or leaf physiology. Here, we investigated the photosynthetic properties of the mid-vein and leaf lamina in a super high-yield hybrid rice (LYP9) during senescence. We found that assimilation and transpiration decreased more slowly in the mid-vein than in the lamina during senescence, suggesting more sustained photosynthesis in the mid-vein, as well as stronger heat dissipation. Two-dimensional gel electrophoresis revealed that the mid-vein had a higher abundance of proteins involved with energy and lower levels of disease or defense-related proteins, suggesting that photosynthesis and energy metabolism were less affected by senescence in the mid-vein than in leaf lamina. In late senescence stage, the excess energy dissipation in the mid-vein through the xanthophyll cycle had a higher active photosynthetic capacity than in the leaf lamina, and we inferred that the mid-vein and leaf lamina of LYP9 rice aged heterogeneously. Taken together, these results provide new insights into the underlying mechanisms of senescence and associated physiology of the rice mid-vein.